I still think there's an opportunity to use a thermal cam to screen a crowd and pick out temperature outliers, but you have to make sure that there isn't obstructing clothing and that the individuals have been in the same conditions for some time (someone coming in out of the cold, for example, would appear an outlier until they come up to temperature with the rest of the crowd).
I took some more pics of my head with my thermal cam and in terms of maximum measurement (closest to core temperature), my best results have been in the mouth, all the way back, on either side of the tongue. I took a couple close ups with the tongue up and down, and surprisingly, much of the underside of the tongue is still well below the temperature of those back corners between the tongue and the side of the mouth. Of course, there is definitely a closeness requirement to get a reasonable resolution picture of your mouth which would still require protective clothing in a disease screening situation, it also doesn't really work noninvasively because they have to have their mouth wide open to be screened. I tried a couple of pictures of the ear and it seems like it would be a real challenge to get a good reading - much harder than through the mouth. Partly because the ear canal isn't straight so you can't really see all the way in, partly because it's tough to focus on it, and partly because it would require even closer contact with the screener.
You can see some variation day to day in relative contrast (and days where the nose isn't cold, for whatever reason) in my images, but it doesn't seem like any features on the exterior of the face are as close to core temperature as the back corners of the mouth, and with a base accuracy of +-2C, even my e40 hacked to e60 wouldn't be that reliable for absolute temperature unless you had a calibration point regularly referenced or in frame. My images were taken indoors with very little airflow in a slightly cool environment. Don't know if they'll be any use, but maybe as a comparison of hotspots or another datapoint to go with pictures of your own face!